Software and Sociology in UK Astronomy

I discuss the remit of Starlink's software strategy groups and a particular item on the agenda of a meeting of the image processing software strategy group held on 26th January 2001: `Why don't people use Starlink software?'. The answer to this question was speculated to be primarily a sociological effect: those people supervising UK astronomy Ph.D. students are largely people who had learnt their trade at a time when Starlink had a less than perfect reputation. I report on the recommendations made to Starlink to counter this effect.Comment: 3 pages. Accepted for publication in Astronomy & Geophysics (formerly QJRAS

How typical is the Coma cluster?

Coma is frequently used as the archetype z~0 galaxy cluster to compare higher redshift work against. It is not clear, however, how representative the Coma cluster is for galaxy clusters of its mass or X-ray luminosity, and significantly: recent works have suggested that the galaxy population of Coma may be in some ways anomolous. In this work, we present a comparison of Coma to an X-ray selected control sample of clusters. We show that although Coma is typical against the control sample in terms of its internal kinematics (substructure and velocity dispersion profile), it has a significantly high (~3sigma) X-ray temperature set against clusters of comparable mass. By de-redshifting our control sample cluster galaxies star-formation rates using a fit to the galaxy main sequence evolution at z < 0.1, we determine that the typical star-formation rate of Coma galaxies as a function of mass is higher than for galaxies in our control sample at a confidence level of > 99 per cent. One way to alleviate this discrepency and bring Coma in-line with the control sample would be to have the distance to Coma to be slightly lower, perhaps through a non-negligible peculiar velocity with respect to the Hubble expansion, but we do not regard this as likely given precision measurements using a variety of approaches. Therefore in summary, we urge caution in using Coma as a z~0 baseline cluster in galaxy evolution studies.Comment: accepted for publication in MNRA

The h-index in Australian Astronomy

The Hirsch (2005) h-index is now widely used as a metric to compare individual researchers. To evaluate it in the context of Australian Astronomy, the h-index for every member of the Astronomical Society of Australia (ASA) is found using NASA's Astrophysics Data System Bibliographic Services (ADS). Percentiles of the h-index distribution are detailed for a variety of categories of ASA members, including students. This enables a list of the top ten Australian researchers by h-index to be produced. These top researchers have h-index values in the range 53<h<77, which is less than that recently reported for the American Astronomical Society Membership. We suggest that membership of extremely large consortia such as SDSS may partially explain the difference. We further suggest that many student ASA members with large h-index values have probably already received their Ph.D.'s and need to upgrade their ASA membership status. To attempt to specify the h-index distribution relative to opportunity, we also detail the percentiles of its distribution by years since Ph.D. award date. This shows a steady increase in h-index with seniority, as can be expected.Comment: Accepted for publication in the Publications of the Astronomical Society of Australi

The evolutionary sequence of post-starburst galaxies

© 2017 The Authors. There are multiple ways in which to select post-starburst galaxies in the literature. In this work, we present a study into how two well-used selection techniques have consequences on observable post-starburst galaxy parameters, such as colour, morphology and environment, and how this affects interpretations of their role in the galaxy duty cycle. We identify a master sample of Hδ strong (EWHδ> 3Å) post-starburst galaxies from the value-added catalogue in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7) over a redshift range 0.01 -2.5Å) but one having an additional cut onEWHα (> -3Å).We examine the differences in observables and AGN fractions to see what effect the Hα cut has on the properties of post-starburst galaxies and what these differing samples can tell us about the duty cycle of post-starburst galaxies. We find that Hδ strong galaxies peak in the 'blue cloud', E+As in the 'green valley' and pure E+As in the 'red sequence'.We also find that pure E+As have a more early-type morphology and a higher fraction in denser environments compared with the Hδ strong and E+A galaxies. These results suggest that there is an evolutionary sequence in the post-starburst phase from blue discy galaxies with residual star formation to passive red early-types

Inter-cluster Filaments of Galaxies Programme: Abundance and Distribution of Filaments in the 2dFGRS Catalogue

Filaments of galaxies are known to stretch between galaxy clusters at all redshifts in a complex manner. In this Letter, we present an analysis of the frequency and distribution of inter-cluster galaxy filaments selected from the 2dF Galaxy Redshift Survey. Out of 805 cluster-cluster pairs, we find at least 40 per cent have bone-fide filaments. We introduce a filament classification scheme and cast the filaments into several types according to their visual morphology: straight (lying on the cluster-cluster axis; 37 per cent), warped or curved (lying off the cluster-cluster axis; 33 per cent), sheets (planar configurations of galaxies; 3 per cent), uniform (1 per cent) and irregular (26 per cent). We find that straight filaments are more likely to reside between close cluster pairs and they become more curved with increasing cluster separation. This curving is toward a larger mass concentration in general. We also show that the more massive a cluster is, the more likely it is to have a larger number of filaments. Our results are found to be consistent with a Lambda cold dark matter cosmology.Comment: 6 pages, 3 figures, accepted for publication in MNRAS letter

The Large Peculiar Velocity of the cD Galaxy in Abell 3653

We present a catalogue of galaxies in Abell 3653 from observations made with the 2dF spectrograph at the Anglo-Australian Telescope. Of the 391 objects observed, we find 111 are bone-fide members of Abell 3653. We show that the cluster has a velocity of cz = 32214 +/- 83 km/s (z=0.10738 +/- 0.00027), with a velocity dispersion typical of rich, massive clusters of sigma_{cz} = 880^{+66}_{-54}. We find that the cD galaxy has a peculiar velocity of 683 +/- 96 km/s in the cluster restframe - some 7sigma away from the mean cluster velocity, making it one of the largest and most significant peculiar velocities found for a cD galaxy to date. We investigate the cluster for signs of substructure, but do not find any significant groupings on any length scale. We consider the implications of our findings on cD formation theories.Comment: 16 pages, including 7 figures and a long table. Accepted for publication in MNRA

The Rarity of Star Formation in Brightest Cluster Galaxies as Measured by WISE

We present the mid-infrared (IR) star formation rates of 245 X-ray selected, nearby (z<0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with L_x > 1x10^44 erg/s. The Wide-Field Infrared Survey Explorer (WISE) AllWISE Data Release provides the first measurement of the 12 micron star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M_sol/yr, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 +/- 0.6 % of local BCGs are (approximately) passively evolving, with star formation rates of <10 M_sol/yr. We find that in general, star formation produces only modest BCG growth at the current epoch.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Pulling out Threads from the Cosmic Tapestry: Defining Filaments of Galaxies

Filaments of galaxies are the dominant feature of modern large scale redshift surveys. They can account for up to perhaps half of the baryonic mass budget of the Universe and their distribution and abundance can help constrain cosmological models. However, there remains no single, definitive way in which to detect, describe and define what filaments are and their extent. This work examines a number of physically motivated, as well as statistical, methods that can be used to define filaments and examines their relative merits.Comment: 12 pages, 6 figures, accepted for publication in PAS